F14.1c — Add restricted-palette, luminance, and playability options

[Flow-Fly]

Parent: #129. Depends on the base guide generator from the previous F14.1 child.

Scope

Add advanced generation controls that let artists deliberately work with limited palettes while keeping normal presets enjoyable.

Implementation

• Support an explicitly supplied restricted palette instead of generating colors.
• Support two mapping modes:
  • color: perceptual color distance, the default;
  • luminance: luminance-only matching for intentionally restrictive ramps.
• Add a deterministic one-pass cleanup for truly isolated single-cell noise without dithering.
• Report a small guide-complexity summary such as paintable cells, palette size, and isolated-cell count.
• Keep all options serializable so the setup can be reproduced after save/load.

Acceptance

• Supplied palettes are never expanded or reordered.
• Luminance mode only chooses colors from the supplied palette.
• Cleanup removes isolated noise in fixtures without changing stable regions.
• Complexity reporting is deterministic.
• Tests cover two-color, monochrome-ramp, and small generated palettes.

Out of scope

Palette-picker UI, dithering, manual region editing, and gameplay.

Verification

• Targeted Vitest coverage
• npm run lint
• git diff --check

[Flow-Fly]

Completed in PR #310. The implementation is merged into develop at b3bf845 and the post-merge CI run 29084411483 passed.